Spotting "the world's greatest arbitrage opportunity," Michael Clemens imagines a world without borders:

Large numbers of people wish to move permanently to another country – more than 40% of adults in the poorest quarter of nations. But most of them are either ineligible for any form of legal movement or face waiting lists of a decade or more. Those giant walls are a human creation, but cause more than just human harm: they hobble the global economy, costing the world roughly half its potential economic product.